1. Field of the Invention
The invention relates to a cooling fan, more particularly to a cooling fan that has a casing and a cover in the form of a circuit board.
2. Description of the Related Art
As shown in FIGS. 1 and 2, a conventional cooling fan 1 includes a casing 11, a fan blade unit 12, a stator 13 with four coil-mounting posts 131 and coils 132 mounted on the coil-mounting posts 131, a circuit board 14 with a substrate 141 and a control circuit 14 disposed on the substrate 141, and a cover 15.
The casing 11 includes a base wall 110, a surrounding wall 114 defining an accommodating space, extending upwardly from a peripheral edge of the base wall 110, and defining a top opening and an outlet 112 for passage of fluid flow therethrough, a shaft 111 extending upwardly from a center of the base wall 110, and a pair of board-mounting posts 113 extending upwardly from the base wall 110 and disposed adjacent to the surrounding wall 114 and opposite to the outlet 112.
The fan blade unit 12 includes an annular hub 121 journalled rotatably to the shaft 111 of the casing 11, a plurality of fan blades 122 extending outwardly from the annular hub 121, and a ring-shaped rotor 123 connected to ends of the fan blades 122.
The cover 15 covers the top opening of the surrounding wall 114 and is formed with a central opening 151 for passage of fluid flow into the accommodating space in the casing 11.
The circuit board 14 is provided with a sensing component 142 for controlling signals supplied to the stator 13 in a conventional manner.
During operation, air flow is introduced into the accommodating space in the casing 11 through the central opening 151 and is discharged through the outlet 112 upon rotation of the fan blade unit 12.